The present invention relates to a brazed structure and a metallized structure in which a substrate is ceramic material containing Si such as silicon nitride and a brazing layer or a metallization layer containing an active metal is bonded to and disposed on the ceramics.
Ceramic body such as silicon nitride, SIALON and silicon carbide has various kinds of characteristics not existing in material such as metals. Due to the above, these have been applied and developed as materials of various kinds of components. For instance, by making use of such characteristics as heat resistance, abrasion resistance and light weight and high mechanical strength, these have been applied in structural and mechanical components. However, ceramic material is inherently brittle. In order to complement such a disadvantage, the ceramic material is generally bonded to and integrated with metallic material to use.
In bonding together ceramics and metal, brazing material (active metal brazing material) containing an active metal such as, for instance, Agxe2x80x94Cuxe2x80x94Ti alloy is used to form in advance an active metal-containing brazing layer on a ceramic body. An active metal-containing brazing layer, after disposing a laminate of respective metal foils, an alloy foil or alloy powder on a silicon nitride, is formed by heat-treatment at temperatures higher than the melting point of the active metal-containing brazing material.
On the other hand, the ceramic material such as silicon nitride, by making use of properties of high electrical insulation, high thermal conductance and high mechanical strength thereof, is applied in electronic components. In this case, with the purpose of forming interconnection layers and circuit networks, a metal layer (metallization layer) containing an active metal such as Agxe2x80x94Cuxe2x80x94Ti alloy is formed on the surface of ceramic body (substrate). Such a metallization layer is formed as identical as the brazing layer is formed. When a metal plate such as copper plate is used for the interconnection layer, an active metal-containing metal layer is used for a brazing layer as well as structural material.
When an active metal-containing metal layer (brazing layer or metallization layer) is formed on a surface of a silicon nitride or the like, in the existing procedure, it is general to heat-treat under conditions. Under the conditions, active metal-containing brazing material or metallization material sufficiently wets and spreads on the surface of the silicon nitride.
However, under the existing condition of heat-treatment, there are cases where bonding strength of the brazing layer or metallization layer, further the mechanical strength after brazing become insufficient. This is due to the existing condition of heat-treatment being set to make small a contact angle (wetting angle) of a metal layer by paying attention to wettability of the metal layer to mainly silicon nitride or the like. According to experiments of the present inventors, it has been made clear that reactions between a ceramic material such as silicon nitride and a metal layer must be fully taken into consideration. Due to the lack of consideration to such points, the existing condition of heat-treatment tends to cause the decrease of bonding strength of the brazing layer or metallization layer.
Further, when an active metal-containing metal layer such as Agxe2x80x94Cuxe2x80x94Ti alloy is formed on a silicon nitride through heat-treatment, it is known that the silicon nitride and the Agxe2x80x94Cuxe2x80x94Ti alloy react to form reaction products such as TiN for instance at the interface thereof. However, it is not tried to control reaction products considering diffusion and wettability of the metal layer.
As described above, in the existing method of forming an active metal-containing metal layer (brazing layer or metallization layer), there are problems. These problems are that bonding strength between ceramic body containing silicon such as silicon nitride, SIALON and silicon carbide and a metal layer, further the strength after brazing when a metal layer being a brazing layer, may be insufficient. From the above, it is desired, without deteriorating diffusivity (wettability) of atoms in a metal layer to a ceramic body containing silicon, to improve the bonding strength or the like of the active metal-containing metal layer as brazing layer or metallization layer with reproducibility.
An object of the present invention is to provide a brazed structure and a metallized structure that enable to improve characteristics such as the bonding strength or the like of an active metal-containing metal layer with reproducibility.
A brazed structure of the present invention comprises a ceramic body containing silicon, an active metal-containing brazing layer, and a reaction layer. The active metal-containing brazing layer is bonded to and disposed on a surface of the ceramic body. The reaction layer is formed at the interface of the ceramic body and the brazing layer and consisting essentially of a compound containing constituent elements of the ceramics and the active metal. Here, the reaction layer exists ahead a front edge line of the brazing layer along a direction into which the brazing layer spreads while wetting.
A metallized structure of the present invention comprises ceramic body containing silicon, an active metal-containing metallization layer, and a reaction layer. The active metal-containing metallization layer is bonded to and disposed on a surface of the ceramic body. The reaction layer is formed at the interface between the ceramic body and the metallization layer and consisting essentially of a compound containing constituent elements of the ceramic body and the active metal. Here, the reaction layer exists ahead a front edge line of the metallization layer along a direction into which the metallization layer spreads while wetting.
In a brazed structure and a metallized structure of the present invention, in more specific, the reaction layer comprises a first reaction layer, and a second reaction layer. The first reaction layer exists more close to the ceramic body than to the brazing layer and consists mainly of a compound made of a non-metallic element of constituent of the ceramic body and an active metal. The second reaction layer exists more close to the brazing layer than to the ceramic body and consists mainly of a compound made of silicon of constituent elements of the ceramic body and an active metal. In the case of the reaction layer having such a structure, the first reaction layer exists ahead of a front edge line of the second reaction layer, or the first reaction layer is formed uniformly.
In a brazed structure and a metallized structure of the present invention, for the ceramic body, one kind selected from, for instance, silicon nitride, SIALON and silicon carbide can be used. In addition, as the active metal, at least one kind selected from, for instance, titanium, zirconium, hafnium, niobium, aluminum, vanadium and tantalum can be used.
In the present invention, a reaction layer consisting of compounds containing constituent elements of the silicon-containing ceramic body and an active metal exists ahead a front edge line of a metal layer as the brazing layer or the metallization layer. Thus, by allowing a reaction layer consisting of compounds that are reaction products of the ceramic body and an active metal to exist ahead in a direction into which the metal layer spreads while wetting (diffusing direction), the bonding strength of the metal layer can be improved with stability.
In particular, by advancing the first reaction layer ahead of the second reaction layer, the metal layer bonded with high strength can be realized with good reproducibility. The first reaction layer largely contributes in improvement of the bonding strength of the ceramic body and the metal layer and consists mainly of a compound of a nonmetallic element of the ceramic body and an active metal such as titanium nitride. The second reaction layer consists mainly of a compound of silicon and an active metal such as titanium silicide. Further, even by forming the first reaction layer uniform, the metal layer bonded with high mechanical strength can be obtained with good reproducibility. When the second reaction layer advances ahead of the first reaction layer, titanium nitride or the like that is a main component of the first reaction layer decreases in its amount. As a result of this, the first reaction layer is likely to be formed discretely to result in deterioration of the bonding strength.